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I can't advise for Ontario backflow requirements, but as long as it can be located higher than the highest sprinkler or pipe downstream, a PVB will be absolute protection for your water supply from a normal sprinkler system's backflow. I would favor a Wilkins 720, as having more reliability.

Inline dual check valves are not for sprinkler system backflow protection...

Boots is absolutely correct... but brisk, I want to explain something that for the longest time confused me.

There is a backflow preventer know as a DCVA (I think that stands for Duel Check Valve backflow Assymbly). At its core, a DC and a DCVA both use a pair of check valves to prevent water from flowing backwards. But a DCVA uses check valves rated for backflow prevention AND additional assymblies that allows the check valves to be tested independantly of one another so that the device can be verified that it is working correctly.

So you can think of it like this... you use a DC when you would LIKE the water to not flow backwards. You use a DCVA when you NEED the water to not flow backwards.

However, there is another thing to consider when it comes to DCVA. The offer the least protection of all the basic types of industry standard backflow prevention. The reason is that the check valves can easily become fouled and quit working. Even more, if there is enough 'stuff' in the water to allow one valve to become fouled, there is a good probability that the second one will get fouled at the same time. When that happens, you go from redundant backflow protection (two valves) to no protection. As such, some people (and some municipalities) do not believe that DCVAs are appropriate protection from an irrigation system.

So while you might want to use a DCVA (after all, they allow the ability of the backflow preventer to be installed underground or indoors), you might not want to or you might not be allowed to (by local building codes) use them.

Let Wetboots answer the backflow preventer question. He's the expert. Also local code should be checked. In my case I bought a Febco PVB and added my own pvc unions. And it had to be at least 12 inches higher that the highest head. But the one in the link does the same thing. Also if you put it in the garage be aware that it may "spit" occasionally.